Meter gets a named Meter interface.

MeterProvider returns the registered global meter provider.

Propagators returns the registered global propagators instance.

SetMeterProvider registers `mp` as the global meter provider.

SetPropagators registers `p` as the global propagators instance.

SetTraceProvider registers `tp` as the global trace provider.

TraceProvider returns the registered global trace provider.

Tracer creates a named tracer that implements Tracer interface.